1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a driving method and apparatus of a plasma display panel in which a screen quality is improved.
2. Description of the Related Art
Recently, a plasma display panel (Hereinafter, referred to as “PDP”) is gaining a popularity as a slim and light display device. The PDP varies light emission times in proportion to a video signal (for example, a television signal) to display an image. In detail, the video signal is digitalized, and digitalized video data is divided into a sub-field period according to a bit number. For each sub-field period, the light emission is performed at the number of times (for example, the number of sustain pulses) proportional to a luminance weighted value of the digital video data to express a grayscale.
For example, in case eight bits of video data are used to express the image using 256 grayscales, as shown in FIG. 1, an expression period for one frame (for example, 1/60 second=about 16.7 msec) is divided into eight sub-fields (SF1 to SF8). Each of the sub-field (SF1 to SF8) is again divided into a reset period (RP), an address period (AP) and a sustain period (SP). Herein, the reset period (RP) and the address period (AP) are identically allocated every sub-field, whileas the sustain period (SP) is increased at a ratio of 1:2:4:8:16:32:64:128.
The PDP driven using the above sub-field driving method duplicates a light emitted from each sub-field to display the image corresponding to a grayscale value.
However, in the conventional PDP driving method, an inconsistency between a visual property perceived by a human eye and an integral direction of the light causes a false contour noise to be generated. The false contour noise is generally observed in a format of a white stripe or a black stripe. The false contour noise is mainly generated in case grayscale levels having greatly different light emission patterns are continuously expressed such as “grayscale 127—grayscale 128”, “grayscale 63—grayscale 64”, “grayscale 3—grayscale 32” and the like. Herein, in case the light emission pattern is varied from a grayscale 128 to a grayscale 127, a brightness difference is “1” between two frames. However, as shown in FIG. 1, all of the 1st to 7th sub-fields (SF1 to SF7) of one frame are emitted in case the grayscale value of 127 is expressed, whileas only the 8th sub-field of one frame is emitted in case the grayscale value of 128 is expressed. That is, in case the light emission pattern is varied from the grayscale 128 to the grayscale 127, the time difference between the light emission patterns between the two frames become large, and the large time difference causes positions of light emission centers between respective frames to be greatly deviated from one another thereby generating the false contour noise.
Accordingly, the conventional art uses a control method of the luminance weighted value every sub-field so as to reduce the false contour noise. That is, the conventional art sets the luminance weighted value every sub-field at a ratio of 1:3:6:12:19:26:34:42:51:61 to reduce the false contour noise (actually, various luminance weighted values are used). If the luminance weighted value is set, the light emission pattern is not varied greatly and accordingly, the false contour noise can be reduced.
However, in case the luminance weighted value is set at the ratio of 1:3:6:12:19:26:34:42:51:61, there is a drawback in that a non-expressible grayscale value is generated thereby reducing a grayscale reappearance. That is, as shown in FIG. 2, when the luminance weighted value is set at the ratio of 1:3:6:12:19:26:34:42:51:61, many grayscales are not expressed including a grayscale of “2”, a grayscale of “5”, a grayscale of “8”, a grayscale of “11” and the like.
Accordingly, in case there is the non-expressible grayscale value using the above-set luminance weighted value, an error diffusion method can be used to express the non-expressible grayscale value. The error diffusion method is a method where a level difference between the non-expressible grayscale value and an expressible grayscale value is spatially diffused to express a certain grayscale value. In order to obtain the certain grayscale value using the error diffusion method, a diffusion circuit of FIG. 3 is used.
FIG. 3 is a view illustrating a conventional error diffusion circuit for performing error diffusion.
Referring to FIG. 3, the conventional error diffusion circuit 20 includes a lookup table 24 and an error diffusion unit 50. The expressible grayscale values using the luminance weighted values (for example, 1:3:6:12:19:26:34:42:51:61) are stored in the lookup table 24 as shown in FIG. 2. The lookup table 24 outputs a certain grayscale value correspondingly to an input grayscale value (data). The lookup table is illustrated as one example.
It does not matter that the lookup table employs any method where the certain grayscale value can be outputted corresponding to the input grayscale value.
The error diffusion unit 50 includes a subtractor 22, a plurality of delay elements 26, 28, 30 and 32, a plurality of multipliers 34, 36, 38 and 40, adders 42 and 44 and the like.
The subtractor 22 subtracts an output grayscale value of the lookup table 24 from the input grayscale value outputted from the adder 44 to output an erroneous value.
The plurality of delay elements 26, 28, 30 and 32 diffuses the erroneous values to peripheral pixels adjacent to a pixel expressing the output grayscale value. That is, the first delay element 26 delays the erroneous value by one pixel to output the delayed value therefrom. At this time, the first delay element 26 includes a memory having a size of storing data of one pixel. The second delay element 28 delays the erroneous value by (one horizontal line+one pixel) to output the delayed value therefrom. At this time, the second delay element 28 includes a memory having a size of storing data of (one horizontal line+one pixel). The third delay element 30 delays the erroneous value by one horizontal line to output the delayed value therefrom. At this time, the third delay element 30 includes a memory having a size of storing data of one horizontal line. The fourth delay element 32 delays the erroneous value by (one horizontal line−one pixel) to output the delayed value therefrom. At this time, the fourth delay element 32 includes a memory having a size of storing data of (one horizontal line−one pixel).
The multipliers 34, 36, 38 and 40 multiply the erroneous values respectively delayed from the plurality of delay elements 26, 28, 30 and 32 with certain coefficient values (K1 to K4) to output the multiplied values therefrom. Herein, the certain coefficient value is set as a value satisfying an equation of K1+K2+K3+K4=1. For example, as shown in FIG. 7, K1, K2, K3 and K4 can be respectively set to 7/16, 1/16, 5/16 and 3/16.
The first adder 42 adds each of the multiplied values outputted from the multipliers 34, 36, 38 and 40 to one another. The second adder 44 adds the grayscale value inputted from an external with the grayscale value (erroneous value) outputted from the first adder 42. The above added grayscale value can be outputted as a corresponding grayscale value by the lookup table 24.
An operation procedure of the diffusion circuit 20 is in detail described.
First, data corresponding to the certain grayscale value is inputted from the external. This grayscale value is inputted to the lookup table 24 via the second adder 44. At this time, the erroneous value outputted from the second adder 44 is regarded to be “0”. In case the input grayscale value is “1”, the lookup table 24 outputs the grayscale value of “1” therefrom. The grayscale value outputted from the lookup table 24 is expressed through a certain pixel on a panel of the PDP. At the same time, the subtractor 22 subtracts the input grayscale value before being inputted to the lookup table 24 and the output grayscale value outputted from the lookup table 24 to provide a certain erroneous value. Herein, since the input grayscale value and the output grayscale value of the lookup table 24 are all “1”, the subtractor 22 outputs the erroneous value corresponding to “0” therefrom. Accordingly, the error diffusion unit 50 no longer performs the error diffusion.
Next, if the grayscale value of “2” is inputted from the external, the grayscale value of “2” does not exist at the lookup table 24. That is, in case the luminance weighted values of FIG. 2 are provided, the grayscale value of “2” cannot be expressed. In this case, the lookup table 24 outputs the grayscale value of “1” that is closest to the grayscale value of “2”. At this time, in case the output grayscale value corresponding to any specific input grayscale value does not exist, the lookup table 24 selects the grayscale value that is closest to the input grayscale value, among the grayscale values less than the input grayscale value, as the output grayscale value. Accordingly, the grayscale value of “1” outputted from the lookup table 24 is expressed through a corresponding pixel.
At this time, the subtractor 22 outputs the erroneous value of “1” obtained by subtracting the grayscale value “1” from the grayscale of “2”.
Additionally, the erroneous value is diffused to the peripheral pixels adjacent to the pixel expressing the grayscale value of “1” by each of the delay elements 26, 28, 30 and 32.
Meanwhile, each of the multipliers 34, 36, 38 and 40 multiplies the erroneous value with predetermined coefficient values 7/16, 1/16, 5/16 and 3/16.
The multiplied erroneous values are all added to one another by the first adder 42, and then are added to a next inputted grayscale value by the second adder 44. The above added grayscale value is again inputted to the lookup table 24.
As described above, the conventional error diffusion circuit spatially diffuses the level difference between grayscale data inputted and grayscale data converted at the lookup table 24. Accordingly, the erroneous value of the adjacent pixels of FIG. 5 is diffused and inputted to the pixels. The error diffusion method is applied to an entire screen of the PDP to be expressed on a human's eye as if an original pixel luminance, that is, a before-conversion grayscale level is expressed. Accordingly, the conventional art can express a high definition image having various grayscale levels without the false contour.
However, since the conventional error diffusion method uses the coefficient values allocated with certain weighted values, that is, 7/16, 1/16, 5/16 and 3/16 to diffuse the error, the patterned noise is generated. In other words, since the error diffusion is performed using a fixed coefficient value such that the error diffusion has a repetition property, the patterned noise is generated. Accordingly, the conventional art has a drawback in that the patterned noise causes the screen quality to be remarkably deteriorated.